Normalized difference chlorophyll index: A novel model for remote estimation of chlorophyll-a concentration in turbid productive waters

a r t i c l e i n f o Keywords: Chlorophyll-a Normalized difference chlorophyll index Remote sensing reflectance Spectral algorithm Turbid productive waters MEdium Resolution Imaging Spectrometer We propose a normalized difference chlorophyll index (NDCI) to predict chlorophyll-a (chl-a) concentration from remote sensing data in estuarine and coastal turbid productive (case 2) waters. NDCI calibration and validation results derived from simulated and MEdium Resolution Imaging Spectrometer (MERIS) datasets show its potential application to widely varying water types and geographic regions. A quadratic function (R 2 =0.95, p b 0.0001) accurately explained the variance in the simulated data for a chl-a range of 1–60 mg m − 3. Similarly a twofold calibration and validation of chl-a models using MERIS dataset, (chl-a range: 0.9–28.1 mg m − 3) yielded R 2 of 0.9, and RMSE of ~2 mg m − 3 respectively. NDCI was applied on images over the Chesapeake Bay and Delaware Bay, the Mobile Bay, and the Mississippi River delta region in the northern Gulf of Mexico. The newly developed algorithm was successful in predicting chl-a concentration with approximately 12% overall bias for all above study regions. Findings from this research imply that NDCI can be successfully used on MERIS images to quantitatively monitor chl-a in inland coastal and estuarine waters. In case of remote coastal waters with no ground truth data, NDCI can be used to detect algal bloom and qualitatively infer chl-a concentration ranges very similar to NDVI's application in terrestrial vegetation studies. Accurate remote estimation of biophysical parameters such as chlorophyll-a (chl-a) and phytoplankton biomass in turbid productive waters is essential for large-scale and multi-temporal studies related to primary production, carbon cycle, biogeochemical cycles, and overall inland and coastal water quality. However, it is still a challenge because of the presence of non-covarying optically active constituents whose absorption features overlap with chl-a. Spectral channels in the blue-green part of the electromagnetic spectrum are heavily affected by the presence of constituents such as Colored Dissolved Organic Matter (CDOM), detritus, and tripton. Empirical algorithms (e.g., OC4v4) that use blue and green spectral channels often provide a relatively accurate estimate of chl-a in case 1 waters where the total non-water absorption is dominated by phytoplankton, however, do not provide reasonable estimates of chl-a in turbid productive waters (O'Reilly et al., 1998). In order to reduce the estimation error of chl-a in turbid productive waters , semi-analytical models have …